(PECL solr >= 0.9.2)
SolrDocument::offsetSet — Adds a field to the document
$fieldName, string $fieldValue): voidUsed when the object is treated as an array to add a field to the document.
fieldNameThe name of the field.
fieldValueThe value for this field.
成功时返回 true, 或者在失败时返回 false。